A septum pellucidum cyst is defined as a fluid collection between the lateral ventricles whose walls have a lateral curvature and are separated by 10 mm or more . Most of these cysts are benign and their clinical significance should be considered as a neurodevelopmental anomaly that may contribute to neuropsychiatric abnormalities . It is often of incidental finding, of little clinical significance. However, an association between this developmental anomaly and a mental disorder, such as schizophrenia and/or intellectual disability, has been reported. We report in this study two clinical cases, diagnosed with schizophrenia comorbid with intellectual disability and in whom brain imaging has objectified a cyst of the septum pellucidum. The objective of this study is to discuss the relationship between the septum pellucidum cyst and mental disorders, especially schizophrenia and intellectual disability.